tl;dr
Book this apartment, you won't be sorry.
Longer version
Tan's apartment turned out to be better than described and depicted on the photos. It has a modern yet very warm design. Noise from the construction happening nearby wasn't that loud and didn't turn out to be an issue. Yes, we have seen homeless people but you get to see them in every country and they didn't harass us in any way, so again - not an issue.
Tan gave us valuable advice about places to eat, drink and visit - he was very helpful, responsive and non-intrusive. He checked on us couple of times during our stay to see if we needed anything. He met us in person which felt welcoming.
Overall, the apartment and Tan's attitude made us feel like home. We have booked via AirBNB over a dozen times all around the world over the past years and our stay at Tan's place is in our top three. The best endorsement might be this though: we have already recommended Tan's place to our friends considering staying in Bangkok.